In this paper, a new
method for discovering the candidate car license plate locations is presented.
First, the image is decomposed using a Haar wavelet to get the HL band with
vertical edges. Then, the HL band image is binarized using an Otsu threshold. Next
a black top-hat algorithm is applied to reduce the effects of interfering large
continuous features other than the license plate. At this time, a moving window
based modified variance score calculation is made for areas with white pixels.
This work found that the top 3 detected rectangle windows correctly locate the
license plate regions with a success rate of about 98.2%. Moreover, the
proposed method is robust enough to locate the plates in cases where the rough
vehicle position has not been previously discovered and the cars are not
centered in the image.

Li, X.P., Lv, X.X., Wang, S.Z., Zhang, L., Li, Y.X. and Dong, H.J. (2010) Research on the Recognition Algorithm of the License Plate Character Based on the Multi-resolution Template Matching. 4th International Conference on New Trends in Information Science and Service Science, Gyeongju, 11-13 May 2010, 341-344.